Appetizing rancidity of apoptotic cells for macrophages: oxidation, externalization, and recognition of phosphatidylserine

Increased unsaturated lipids underlie lipid peroxidation in synucleinopathy brain

Lipid peroxidation is a process of oxidative degradation of cellular lipids that is increasingly recognized as an important factor in the pathogenesis of neurodegenerative diseases. We were therefore interested in the manifestation of lipid peroxidation in synucleinopathies, a group of neurodegenerative diseases characterized by the central pathology of α-synuclein aggregates, including Parkinson's disease, multiple system atrophy, dementia with Lewy bodies and Alzheimer's disease with Lewy bodies. We assessed lipid peroxidation products, lipid aldehydes, in the amygdala, a common disease-affected region in synucleinopathies, and in the visual cortex, a disease-unaffected region. We found that the levels of lipid aldehydes were significantly increased in the amygdala, but not in the visual cortex. We hypothesized that these increases are due to increases in the abundance of unsaturated lipids, since lipid aldehydes are formed from unsaturated lipids. We undertook a comprehensive analysis of membrane lipids using liquid chromatography-mass spectrometry and found that unsaturated phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and sphingomyelin were specifically elevated in the amygdala and correlated with increases in lipid aldehydes. Furthermore, unsaturated phosphatidylethanolamine levels were associated with soluble α-synuclein. Put together, these results suggest that manifestation of lipid peroxidation is prevalent in synucleinopathies and is likely to be due to increases in unsaturated membrane lipids. Our findings underscore the importance of lipid peroxidation in α-synuclein pathology and in membrane structure maintenance.

Prognostic value of hemoglobin-to-red cell distribution width ratio in cancer: a systematic review and meta-analysis

Background: The hemoglobin-to-red cell distribution width ratio (HRR) has emerged as a novel integrative biomarker predictive of overall and disease-free survival in cancer patients. This study aimed to investigate the prognostic significance of HRR in the cancer population. Methods: A literature search was performed in PubMed/MEDLINE from inception to 1 July 2021, to collect studies assessing the prognostic value of HRR in cancer patients. The primary and secondary end points were all-cause mortality and occurrence of disease progression or relapse, respectively. A meta-analytic approach was employed to estimate the pooled hazard ratio with 95% CI by fitting random-effects models. Results: A total of 11 retrospective cohort studies representing 2985 cancer patients were included. Compared with patients with high HRR, patients with low HRR had a twofold risk of all-cause mortality (hazard ratio: 2.29; 95% CI: 1.76-2.98; p < 0.0001). There was substantial heterogeneity in the association of HRR with mortality across the studies (I²: 66.8%; 95% CI: 35.3-82.9%; p = 0.0014). Similarly, low HRR was associated with a twofold risk of disease progression or relapse (hazard ratio: 2.19; 95% CI: 1.74-2.76; p < 0.0001). No significant heterogeneity was observed (I²: 16.8%; 95% CI: 0.0-60.7%; p = 0.30). Conclusion: Low HRR was associated with mortality and disease progression or relapse in patients with cancer. Further studies are required to standardize the HRR cutoff value and investigate whether HRR can be incorporated into risk assessment models for predicting adverse prognosis in cancer patients.

Screening of Lipids for Early Triage and Dose Estimation after Acute Radiation Exposure in Rat Plasma Based on Targeted Lipidomics Analysis

Rapid early triage and dose estimation is vital for limited medical resource allocation and treatment of a large number of the wounded after radiological accidents. Lipidomics has been utilized to delineate biofluid lipid signatures after irradiation. Here, high-coverage targeted lipidomics was employed to screen radiosensitive lipids after 0, 1, 2, 3, 5, and 8 Gy total body irradiation at 4, 24, and 72 h postirradiation in rat plasma. Ultra-performance liquid chromatography-tandem mass spectrometry with a multiple reaction monitoring method was utilized. In total, 416 individual lipids from 18 major classes were quantified and those biomarkers altered in a dose-dependent manner constituted panel A-panel D. Receiver operator characteristic curve analysis using combined lipids showed good to excellent sensitivity and specificity in triaging different radiation exposure levels (area under curve = 0.814-1.000). The equations for dose estimation were established by stepwise regression analysis for three time points. A novel strategy for radiation early triage and dose estimation was first established and validated using panels of lipids. Our study suggests that it is feasible to acquire quantitative lipid biomarker panels using targeted lipidomics platforms for rapid, high-throughput triage, which can provide further insights in developing lipidomics strategies for radiation biodosimetry in humans.

Radiolabeled Peptides for Molecular Imaging of Apoptosis

Apoptosis is a regulated cell death induced by extrinsic and intrinsic stimulants. Tracking of apoptosis provides an opportunity for the assessment of cardiovascular and neurodegenerative diseases as well as monitoring of cancer therapy at early stages. There are some key mediators in apoptosis cascade, which could be considered as specific targets for delivering imaging or therapeutic agents. The targeted radioisotope-based imaging agents are able to sensitively detect the physiological signal pathways which make them suitable for apoptosis imaging at a single-cell level. Radiopeptides take advantage of both the high sensitivity of nuclear imaging modalities and favorable features of peptide scaffolds. The aim of this study is to review the characteristics of those radiopeptides targeting apoptosis with different mechanisms.

Development of a highly sensitive detection method for TTX based on a magnetic bead-aptamer competition system under triple cycle amplification

We have established an assay that relies on aptamer and isothermal amplification for the tetrodotoxin (TTX)detection. The method uses triple cycle amplification (strand displacement amplification combined with catalytic hairpin assembly) and fluorescent reporter as an output signal. Free TTX and cDNA compete for binding to aptamer-modified magnetic beads. The cDNA collected by magnetic separation then used as a primer to trigger triple cycle amplification to obtain more ssDNA. The ssDNA combined with the reporter probe, and the original quenched fluorescence can be recovered. In addition, a linear relationship between fluorescence spectrum and different target concentrations is revealed. This method allows TTX to be detected by fluorometry with a detection limit as low as 0.265 pg mL^-1. It was applied to clams and shellfish, achieving recoveries ranging from 100% to 107.33% and 99.67%-116.67%, respectively. The results were consistent with the commercial TTX ELISA kit. This assay is highly sensitive, reliable and has a good specificity. Therefore, it provides a better alternative to the standard method for quantitative detection of TTX.

Phagocytosis: Phenotypically Simple Yet a Mechanistically Complex Process

Phagocytosis is a pivotal immunological process, and its discovery by Elia Metchnikoff in 1882 was a step toward the establishment of the innate immune system as a separate branch of immunology. Elia Metchnikoff received the Nobel Prize in physiology and medicine for this discovery in 1908. Since its discovery almost 140 years before, phagocytosis remains the hot topic of research in immunology. The phagocytosis research has seen a great advancement since its first discovery. Functionally, phagocytosis is a simple immunological process required to engulf and remove pathogens, dead cells and tumor cells to maintain the immune homeostasis. However, mechanistically, it is a very complex process involving different mechanisms, induced and regulated by several pattern recognition receptors, soluble pattern recognition molecules, scavenger receptors (SRs) and opsonins. These mechanisms involve the formation of phagosomes, their maturation into phagolysosomes causing pathogen destruction or antigen synthesis to present them to major histocompatibility complex molecules for activating an adaptive immune response. Any defect in this mechanism may predispose the host to certain infections and inflammatory diseases (autoinflammatory and autoimmune diseases) along with immunodeficiency. The article is designed to discuss its mechanistic complexity at each level, varying from phagocytosis induction to phagolysosome resolution.

Redox (phospho)lipidomics of signaling in inflammation and programmed cell death

In addition to the known prominent role of polyunsaturated (phospho)lipids as structural blocks of biomembranes, there is an emerging understanding of another important function of these molecules as a highly diversified signaling language utilized for intra- and extracellular communications. Technological developments in high-resolution mass spectrometry facilitated the development of a new branch of metabolomics, redox lipidomics. Analysis of lipid peroxidation reactions has already identified specific enzymatic mechanisms responsible for the biosynthesis of several unique signals in response to inflammation and regulated cell death programs. Obtaining comprehensive information about millions of signals encoded by oxidized phospholipids, represented by thousands of interactive reactions and pleiotropic (patho)physiological effects, is a daunting task. However, there is still reasonable hope that significant discoveries, of at least some of the important contributors to the overall overwhelmingly complex network of interactions triggered by inflammation, will lead to the discovery of new small molecule regulators and therapeutic modalities. For example, suppression of the production of AA-derived pro-inflammatory mediators, HXA3 and LTB4, by an iPLA2 γ inhibitor, R-BEL, mitigated injury associated with the activation of pro-inflammatory processes in animals exposed to whole-body irradiation. Further, technological developments promise to make redox lipidomics a powerful approach in the arsenal of diagnostic and therapeutic instruments for personalized medicine of inflammatory diseases and conditions.

"Only a Life Lived for Others Is Worth Living": Redox Signaling by Oxygenated Phospholipids in Cell Fate Decisions

SIGNIFICANCE

Oxygenated polyunsaturated lipids are known to play multi-functional roles as essential signals coordinating metabolism and physiology. Among them are well-studied eicosanoids and docosanoids that are generated via phospholipase A2 hydrolysis of membrane phospholipids and subsequent oxygenation of free polyunsaturated fatty acids (PUFA) by cyclooxygenases and lipoxygenases. Recent Advances: There is an emerging understanding that oxygenated PUFA-phospholipids also represent a rich signaling language with yet-to-be-deciphered details of the execution machinery-oxygenating enzymes, regulators, and receptors. Both free and esterified oxygenated PUFA signals are generated in cells, and their cross-talk and inter-conversion through the de-acylation/re-acylation reactions is not sufficiently explored.

CRITICAL ISSUES

Here, we review recent data related to oxygenated phospholipids as important damage signals that trigger programmed cell death pathways to eliminate irreparably injured cells and preserve the health of multicellular environments. We discuss the mechanisms underlying the trans-membrane redistribution and generation of oxygenated cardiolipins in mitochondria by cytochrome c as pro-apoptotic signals. We also consider the role of oxygenated phosphatidylethanolamines as proximate pro-ferroptotic signals.

FUTURE DIRECTIONS

We highlight the importance of sequential processes of phospholipid oxygenation and signaling in disease contexts as opportunities to use their regulatory mechanisms for the identification of new therapeutic targets.

Modulation of the inflammatory response of immune cells in human peripheral blood by oxidized arachidonoyl aminophospholipids

Aminophospholipids (APL), phosphatidylethanolamine (PE) and phosphatidylserine (PS), can be oxidized upon oxidative stress. Oxidized PE and PS have been detected in clinical samples of different pathologies and may act as modulators of the inflammatory response. However, few studies have focused on the effects of oxidized APL (ox-APL) esterified with arachidonic acid, even though a considerable number of studies have assessed the modulation of the immune system by oxidized 1-palmitoyl-2-arachidonoyl-sn-3-glycerophosphocholine (OxPAPC). In the present study, we have used flow cytometry to evaluate the ability of oxidized PAPE (OxPAPE) and PAPS (OxPAPS) to promote or suppress an inflammatory phenotype on monocytes subsets and myeloid dendritic cells (mDCs). The results indicate that OxPAPE increases the frequency of all monocyte subpopulations expressing TNF-α, which promotes an inflammatory response. However, immune cell stimulation with OxPAPE in the presence of LPS results in a decrease of TNF-α expressed by classical monocytes. Incubation with OxPAPS and LPS induces a decrease in TNF-α produced by monocytes, and a significant decrease in IL-1β expressed by monocytes and mDCs, indicating that OxPAPS reduces the LPS-induced pro-inflammatory expression in these populations. These results show the importance of OxPAPE and OxPAPS as modulators of the inflammatory response and demonstrate their possible contribution to the onset and resolution of human diseases related to oxidative stress and inflammation.

Efferocytosis of dying cells differentially modulate immunological outcomes in tumor microenvironment

Programmed cell death (apoptosis) is an integral part of tissue homeostasis in complex organisms, allowing for tissue turnover, repair, and renewal while simultaneously inhibiting the release of self antigens and danger signals from apoptotic cell-derived constituents that can result in immune activation, inflammation, and autoimmunity. Unlike cells in culture, the physiological fate of cells that die by apoptosis in vivo is their rapid recognition and engulfment by phagocytic cells (a process called efferocytosis). To this end, apoptotic cells express specific eat-me signals, such as externalized phosphatidylserine (PS), that are recognized in a specific context by receptors to initiate signaling pathways for engulfment. The importance of carefully regulated recognition and clearance pathways is evident in the spectrum of inflammatory and autoimmune disorders caused by defects in PS receptors and signaling molecules. However, in recent years, several additional cell death pathways have emerged, including immunogenic cell death, necroptosis, pyroptosis, and netosis that interweave different cell death pathways with distinct innate and adaptive responses from classical apoptosis that can shape long-term host immunity. In this review, we discuss the role of different cell death pathways in terms of their immune potential outcomes specifically resulting in specific cell corpse/phagocyte interactions (phagocytic synapses) that impinge on host immunity, with a main emphasis on tolerance and cancer immunotherapy.

Avenues to molecular imaging of dying cells: Focus on cancer

Successful treatment of cancer patients requires balancing of the dose, timing, and type of therapeutic regimen. Detection of increased cell death may serve as a predictor of the eventual therapeutic success. Imaging of cell death may thus lead to early identification of treatment responders and nonresponders, and to “patient‐tailored therapy.” Cell death in organs and tissues of the human body can be visualized, using positron emission tomography or single‐photon emission computed tomography, although unsolved problems remain concerning target selection, tracer pharmacokinetics, target‐to‐nontarget ratio, and spatial and temporal resolution of the scans. Phosphatidylserine exposure by dying cells has been the most extensively studied imaging target. However, visualization of this process with radiolabeled Annexin A5 has not become routine in the clinical setting. Classification of death modes is no longer based only on cell morphology but also on biochemistry, and apoptosis is no longer found to be the preponderant mechanism of cell death after antitumor therapy, as was earlier believed. These conceptual changes have affected radiochemical efforts. Novel probes targeting changes in membrane permeability, cytoplasmic pH, mitochondrial membrane potential, or caspase activation have recently been explored. In this review, we discuss molecular changes in tumors which can be targeted to visualize cell death and we propose promising biomarkers for future exploration.

The Reactive Oxygen Species in Macrophage Polarization: Reflecting Its Dual Role in Progression and Treatment of Human Diseases

High heterogeneity of macrophage is associated with its functions in polarization to different functional phenotypes depending on environmental cues. Macrophages remain in balanced state in healthy subject and thus macrophage polarization may be crucial in determining the tissue fate. The two distinct populations, classically M1 and alternatively M2 activated, representing the opposing ends of the full activation spectrum, have been extensively studied for their associations with several disease progressions. Accumulating evidences have postulated that the redox signalling has implication in macrophage polarization and the key roles of M1 and M2 macrophages in tissue environment have provided the clue for the reasons of ROS abundance in certain phenotype. M1 macrophages majorly clearing the pathogens and ROS may be crucial for the regulation of M1 phenotype, whereas M2 macrophages resolve inflammation which favours oxidative metabolism. Therefore how ROS play its role in maintaining the homeostatic functions of macrophage and in particular macrophage polarization will be reviewed here. We also review the biology of macrophage polarization and the disturbance of M1/M2 balance in human diseases. The potential therapeutic opportunities targeting ROS will also be discussed, hoping to provide insights for development of target-specific delivery system or immunomodulatory antioxidant for the treatment of ROS-related diseases.

Cardiolipin signaling mechanisms: collapse of asymmetry and oxidation

SIGNIFICANCE

An ancient anionic phospholipid, cardiolipin (CL), ubiquitously present in prokaryotic and eukaryotic membranes, is essential for several structural and functional purposes.

RECENT ADVANCES

The emerging role of CLs in signaling has become the focus of many studies.

CRITICAL ISSUES

In this work, we describe two major pathways through which mitochondrial CLs may fulfill the signaling functions via utilization of their (i) asymmetric distribution across membranes and translocations, leading to the surface externalization and (ii) ability to undergo oxidation reactions to yield the signature products recognizable by the executionary machinery of cells.

FUTURE DIRECTIONS

We present a concept that CLs and their oxidation/hydrolysis products constitute a rich communication language utilized by mitochondria of eukaryotic cells for diversified regulation of cell physiology and metabolism as well as for inter-cellular interactions.

A lysine-rich motif in the phosphatidylserine receptor PSR-1 mediates recognition and removal of apoptotic cells

The conserved phosphatidylserine receptor (PSR) was first identified as a receptor for phosphatidylserine, an 'eat-me' signal exposed by apoptotic cells. However, several studies suggest that PSR may also act as an arginine demethylase, a lysyl hydroxylase, or an RNA-binding protein through its N-terminal JmjC domain. How PSR might execute drastically different biochemical activities, and whether they are physiologically significant, remain unclear. Here we report that a lysine-rich motif in the extracellular domain of PSR-1, the Caenorhabditis elegans PSR, mediates specific phosphatidylserine binding in vitro and clearance of apoptotic cells in vivo. This motif also mediates phosphatidylserine-induced oligomerization of PSR-1, suggesting a mechanism by which PSR-1 activates phagocytosis. Mutations in the phosphatidylserine-binding motif, but not in its Fe(II) binding site critical for the JmjC activity, abolish PSR-1 phagocytic function. Moreover, PSR-1 enriches and clusters around apoptotic cells during apoptosis. These results establish that PSR-1 is a conserved, phosphatidylserine-recognizing phagocyte receptor.

Respiratory risks from household air pollution in low and middle income countries

A third of the world's population uses solid fuel derived from plant material (biomass) or coal for cooking, heating, or lighting. These fuels are smoky, often used in an open fire or simple stove with incomplete combustion, and result in a large amount of household air pollution when smoke is poorly vented. Air pollution is the biggest environmental cause of death worldwide, with household air pollution accounting for about 3·5-4 million deaths every year. Women and children living in severe poverty have the greatest exposures to household air pollution. In this Commission, we review evidence for the association between household air pollution and respiratory infections, respiratory tract cancers, and chronic lung diseases. Respiratory infections (comprising both upper and lower respiratory tract infections with viruses, bacteria, and mycobacteria) have all been associated with exposure to household air pollution. Respiratory tract cancers, including both nasopharyngeal cancer and lung cancer, are strongly associated with pollution from coal burning and further data are needed about other solid fuels. Chronic lung diseases, including chronic obstructive pulmonary disease and bronchiectasis in women, are associated with solid fuel use for cooking, and the damaging effects of exposure to household air pollution in early life on lung development are yet to be fully described. We also review appropriate ways to measure exposure to household air pollution, as well as study design issues and potential effective interventions to prevent these disease burdens. Measurement of household air pollution needs individual, rather than fixed in place, monitoring because exposure varies by age, gender, location, and household role. Women and children are particularly susceptible to the toxic effects of pollution and are exposed to the highest concentrations. Interventions should target these high-risk groups and be of sufficient quality to make the air clean. To make clean energy available to all people is the long-term goal, with an intermediate solution being to make available energy that is clean enough to have a health impact.

Redox control of inflammation in macrophages

Macrophages are present throughout the human body, constitute important immune effector cells, and have variable roles in a great number of pathological, but also physiological, settings. It is apparent that macrophages need to adjust their activation profile toward a steadily changing environment that requires altering their phenotype, a process known as macrophage polarization. Formation of reactive oxygen species (ROS), derived from NADPH-oxidases, mitochondria, or NO-producing enzymes, are not necessarily toxic, but rather compose a network signaling system, known as redox regulation. Formation of redox signals in classically versus alternatively activated macrophages, their action and interaction at the level of key targets, and the resulting physiology still are insufficiently understood. We review the identity, source, and biological activities of ROS produced during macrophage activation, and discuss how they shape the key transcriptional responses evoked by hypoxia-inducible transcription factors, nuclear-erythroid 2-p45-related factor 2 (Nrf2), and peroxisome proliferator-activated receptor-γ. We summarize the mechanisms how redox signals add to the process of macrophage polarization and reprogramming, how this is controlled by the interaction of macrophages with their environment, and addresses the outcome of the polarization process in health and disease. Future studies need to tackle the option whether we can use the knowledge of redox biology in macrophages to shape their mediator profile in pathophysiology, to accelerate healing in injured tissue, to fight the invading pathogens, or to eliminate settings of altered self in tumors.

Oxidized phosphatidylcholines in membrane-level cellular signaling: from biophysics to physiology and molecular pathology

The oxidation of lipids has been shown to impact virtually all cellular processes. The paradigm has been that this involvement is due to interference with the functions of membrane-associated proteins. It is only recently that methodological advances in molecular-level detection and identification have begun to provide insights into oxidative lipid modification and its involvement in cell signaling as well as in major diseases and inflammation. Extensive evidence suggests a correlation between lipid peroxidation and degenerative neurological diseases such as Parkinson's and Alzheimer's, as well as type 2 diabetes and cancer. Despite the obvious relevance of understanding the molecular basis of the above ailments, the exact modes of action of oxidized lipids have remained elusive. In this minireview, we summarize recent findings on the biophysical characteristics of biomembranes following oxidative derivatization of their lipids, and how these altered properties are involved in both physiological processes and major pathological conditions. Lipid-bearing, oxidatively truncated and functionalized acyl chains are known to modify membrane bulk physical properties, such as thermal phase behavior, bilayer thickness, hydration and polarity profiles, as manifest in the altered structural dynamics of lipid bilayers, leading to augmented membrane permeability, fast lipid transbilayer diffusion (flip-flop), loss of lipid asymmetry (scrambling) and phase segregation (the formation of 'rafts'). These changes, together with the generated reactive lipid derivatives, can be further expected to interfere with lipid-protein interactions, influencing metabolic pathways, causing inflammation, the execution phase in apoptosis and initiating pathological processes.

Escherichia coli induces bovine neutrophil cell death independent from caspase-3/-7/-1, but with phosphatidylserine exposure prior to membrane rupture

Neutrophils are essential for the innate immune response against bacterial pathogens and play a key role during the early phases of infection, including mastitis and endometritis in cows. When directly challenged with bacteria, neutrophils undergo phagocytosis induced cell death (PICD). The molecular mechanisms of this cell death modality are poorly understood, especially for bovine neutrophils. Therefore, this study aimed to determine the mechanisms and hallmarks of PICD in bovine neutrophils after in vitro challenge with Escherichia coli (E. coli). Our data show that various apoptotic hallmarks such as blebbing, chromatin condensation and executioner caspase (C)-3/-7 activity are only observed during constitutive bovine neutrophil apoptosis. In contrast, bovine neutrophil PICD is characterized by production of reactive oxygen species (ROS), pro-inflammatory C-1 activation, nuclear factor (NF)-κB activation, and interleukin (IL)-1β and IL-6 secretion. Nevertheless, under both conditions these phagocytes undergo cell death with the exposure of phosphatidylserine (PS). Although PS exposure is generally attributed to the anti-inflammatory features of executioner caspase-dependent apoptosis, it surprisingly preceded plasma membrane rupture during bovine neutrophil PICD. Moreover, C-1 inhibition strongly affected IL-1β production but not the PICD kinetics. This indicates that the secretion of the latter pro-inflammatory cytokine is a bystander effect rather than a regulator of PICD in bovine neutrophils, in marked contrast to the IL-1β-dependent pyroptosis reported for macrophages.

Protein-oxidized phospholipid interactions in cellular signaling for cell death: from biophysics to clinical correlations

Oxidative stress is associated with several major ailments. However, it is only recently that the developments in our molecular level understanding of the consequences of oxidative stress in modifying the chemical structures of biomolecules, lipids in particular, are beginning to open new emerging insights into the significance of oxidative stress in providing mechanistic insights into the etiologies of these diseases. In this brief review we will first discuss the role of lipid oxidation in controlling the membrane binding of cytochrome c, a key protein in the control of apoptosis. We then present an overview of the impact of oxidized phospholipids on the biophysical properties of lipid bilayers and continue to discuss, how these altered properties can account for the observed enhancement of formation of intermediate state oligomers by cytotoxic amyloid forming peptides associated with pathological conditions as well as host defense peptides of innate immunity. In the third part, we will discuss how the targeting of oxidized phospholipids by i) pathology associated peptides and ii) host defense peptides can readily explain the observed clinical correlations associating Alzheimer's and Parkinson's diseases with increased risk for type 2 diabetes and age-related macular degeneration, and the apparent protective effect of Alzheimer's and Parkinson's diseases from some cancers, as well as the inverse, apparent protection by cancer from Alzheimer's and Parkinson's diseases. This article is part of a Special Issue entitled: Oxidized phospholipids-Their properties and interactions with proteins.

Mechanisms of carbon nanotube-induced toxicity: focus on oxidative stress

Nanotechnologies are emerging as highly promising technologies in many sectors in the society. However, the increasing use of engineered nanomaterials also raises concerns about inadvertent exposure to these materials and the potential for adverse effects on human health and the environment. Despite several years of intensive investigations, a common paradigm for the understanding of nanoparticle-induced toxicity remains to be firmly established. Here, the so-called oxidative stress paradigm is scrutinized. Does oxidative stress represent a secondary event resulting inevitably from disruption of biochemical processes and the demise of the cell, or a specific, non-random event that plays a role in the induction of cellular damage e.g. apoptosis? The answer to this question will have important ramifications for the development of strategies for mitigation of adverse effects of nanoparticles. Recent examples of global lipidomics studies of nanoparticle-induced tissue damage are discussed along with proteomics and transcriptomics approaches to achieve a comprehensive understanding of the complex and interrelated molecular changes in cells and tissues exposed to nanoparticles. We also discuss instances of non-oxidative stress-mediated cellular damage resulting from direct physical interference of nanomaterials with cellular structures.

Dynamic monitoring of metal oxide nanoparticle toxicity by label free impedance sensing

The increased use of nanoparticles in industrial and medical products is driving the need for accurate, high throughput in vitro testing procedures to screen new particles for potential toxicity. While approaches using standard viability assays have been widely used, there have been increased reports of the interactions of nanoparticles with their soluble labels or optical readouts which raise concerns over the potential generation of false positive results. Here, we describe the use of an impedance spectroscopy approach to provide real-time reagent free detection of toxicity for a panel of metal oxide nanoparticles (ZnO, CuO, and TiO(2)). Using this approach, we show how impedance measurements can be used to track nanoparticle toxicity over time with comparable IC(50) values to those of standard assays (ZnO-55 μg/mL, CuO-28 μg/mL) as well as being used to identify a critical 6 h period following exposure during which the nanoparticles trigger rapid cellular responses. Through targeted analysis during this response period and the use of a novel image analysis approach, we show how the ZnO and CuO nanoparticles trigger the active export of intracellular glutathione via an increase in the activity of the ATP dependent MRP/1 efflux pumps. The loss of glutathione leads to increased production of reactive oxygen species which after 2.5 h triggers the cells to enter apoptosis resulting in a dose dependent cytotoxic response. This targeted testing strategy provides comprehensive information beyond that achieved with standard toxicity assays and indicates the potential for cell-nanoparticle interactions that could occur following in vivo exposure.

Role of adaptive immunity in alcoholic liver disease

Stimulation of innate immunity is increasingly recognized to play an important role in the pathogenesis of alcoholic liver disease (ALD), while the contribution of adaptive immunity has received less attention. Clinical and experimental data show the involvement of Th-1 and Th-17 T-lymphocytes in alcoholic hepatitis. Nonetheless, the mechanisms by which alcohol triggers adaptive immunity are still incompletely characterized. Patients with advanced ALD have circulating IgG and T-lymphocytes recognizing epitopes derived from protein modification by hydroxyethyl free radicals and end products of lipid-peroxidation. High titers of IgG against lipid peroxidation-derived antigens are associated with an increased hepatic production of proinflammatory cytokines/chemokines. Moreover, the same antigens favor the breaking of self-tolerance towards liver constituents. In particular, autoantibodies against cytochrome P4502E1 (CYP2E1) are evident in a subset of ALD patients. Altogether these results suggest that allo- and autoimmune reactions triggered by oxidative stress might contribute to hepatic inflammation during the progression of ALD.

Mitochondrial injury after mechanical stretch of cortical neurons in vitro: biomarkers of apoptosis and selective peroxidation of anionic phospholipids

Mechanical injury of neurites accompanied by rupture of mitochondrial membranes may lead to immediate nonspecific release and spreading of pro-apoptotic factors and activation of proteases, that is, execution of apoptotic program. In the current work, we studied the time course of the major biomarkers of apoptosis as they are induced by exposure of rat cortical neurons to mechanical stretch. By using transmission electron microscopy, we found that mitochondria in the neurites were damaged early (1 h) after mechanical stretch injury whereas somal mitochondria were significantly more resistant and demonstrated structural damage and degenerative mitochondrial changes at a later time point after stretch (12 h). We also report that the stretch injury caused immediate activation of reactive oxygen species production followed by selective oxidation of a mitochondria-specific phospholipid, cardiolipin, whose individual peroxidized molecular species have been identified and quantified by electrospray ionization mass spectrometry analysis. Most abundant neuronal phospholipids - phosphatidylcholine, phophatidylethanolamine - did not undergo oxidative modification. Simultaneously, a small-scale release of cytochrome c was observed. Notably, caspase activation and phosphatidylserine externalization - two irreversible apoptotic events designating a point of no return - are substantially delayed and do not occur until 6-12 h after the initial impact. The early onset of reactive oxygen species production and cytochrome c release may be relevant to direct stretch-induced damage to mitochondria. The delayed emergence of apoptotic neuronal death after the immediate mechanical damage to mitochondria suggests a possible window of opportunity for targeted therapies.

Global phospholipidomics analysis reveals selective pulmonary peroxidation profiles upon inhalation of single-walled carbon nanotubes

It is commonly believed that nanomaterials cause nonspecific oxidative damage. Our mass spectrometry-based oxidative lipidomics analysis of all major phospholipid classes revealed highly selective patterns of pulmonary peroxidation after inhalation exposure of mice to single-walled carbon nanotubes. No oxidized molecular species were found in the two most abundant phospholipid classes: phosphatidylcholine and phosphatidylethanolamine. Peroxidation products were identified in three relatively minor classes of anionic phospholipids, cardiolipin, phosphatidylserine, and phosphatidylinositol, whereby oxygenation of polyunsaturated fatty acid residues also showed unusual substrate specificity. This nonrandom peroxidation coincided with the accumulation of apoptotic cells in the lung. A similar selective phospholipid peroxidation profile was detected upon incubation of a mixture of total lung lipids with H(2)O(2)/cytochrome c known to catalyze cardiolipin and phosphatidylserine peroxidation in apoptotic cells. The characterized specific phospholipid peroxidation signaling pathways indicate new approaches to the development of mitochondria-targeted regulators of cardiolipin peroxidation to protect against deleterious effects of pro-apoptotic effects of single-walled carbon nanotubes in the lung.

Oxidative lipidomics of γ-radiation-induced lung injury: mass spectrometric characterization of cardiolipin and phosphatidylserine peroxidation

Oxidative damage plays a significant role in the pathogenesis of γ-radiation-induced lung injury. Endothelium is a preferred target for early radiation-induced damage and apoptosis. Given the newly discovered role of oxidized phospholipids in apoptotic signaling, we performed oxidative lipidomics analysis of phospholipids in irradiated mouse lungs and cultured mouse lung endothelial cells. C57BL/6NHsd female mice were subjected to total-body irradiation (10 Gy, 15 Gy) and euthanized 24 h thereafter. Mouse lung endothelial cells were analyzed 48 h after γ irradiation (15 Gy). We found that radiation-induced apoptosis in vivo and in vitro was accompanied by non-random oxidation of phospholipids. Cardiolipin and phosphatidylserine were the major oxidized phospholipids, while more abundant phospholipids (phosphatidylcholine, phosphatidylethanolamine) remained non-oxidized. Electrospray ionization mass spectrometry analysis revealed the formation of cardiolipin and phosphatidylserine oxygenated molecular species in the irradiated lung and cells. Analysis of fatty acids after hydrolysis of cardiolipin and phosphatidylserine by phospholipase A(2) revealed the presence of mono-hydroperoxy and/or mono-hydroxy/mono-epoxy, mono-hydroperoxy/mono-oxo molecular species of linoleic acid. We speculate that cyt c-driven oxidations of cardiolipin and phosphatidylserine associated with the execution of apoptosis in pulmonary endothelial cells are important contributors to endothelium dysfunction in γ-radiation-induced lung injury.

Apoptosis-induced changes in mitochondrial lipids

Apoptosis is an active and tightly regulated form of cell death, which can also be considered a stress-induced process of cellular communication. Recent studies reveal that the lipid network within cells is involved in the regulation and propagation of death signalling. Despite the vast growth of our current knowledge on apoptosis, little is known of the specific role played by lipid molecules in the central event of apoptosis-the piercing of mitochondrial membranes. Here we review the information regarding changes in mitochondrial lipids that are associated with apoptosis and discuss whether they may be involved in the permeabilization of mitochondria to release their apoptogenic factors, or just lie downstream of this permeabilization leading to the amplification of caspase activation. We focus on the earliest changes that physiological apoptosis induces in mitochondrial membranes, which may derive from an upstream alteration of phospholipid metabolism that reverberates on the mitochondrial re-modelling of their characteristic lipid, cardiolipin. Hopefully, this review will lead to an increased understanding of the role of mitochondrial lipids in apoptosis and also help revealing new stress sensing mechanisms in cells. This article is part of a Special Issue entitled Mitochondria: the deadly organelle.

Programmed cell clearance: molecular regulation of the elimination of apoptotic cell corpses and its role in the resolution of inflammation

Programmed cell clearance is a physiological process of elimination of apoptotic cell corpses. Recent studies have disclosed several ligand-receptor interactions that dictate the recognition or non-recognition of cells by macrophages and other phagocytes. The externalization of the anionic phospholipid, phosphatidylserine is effectively recognized by specific receptors on professional phagocytes and facilitates the clearance of apoptotic cells. Macrophage disposal of cells at sites of inflammation is believed to play an important role in the resolution of the inflammatory process, and recent studies have suggested a role for the NADPH oxidase in the process of macrophage elimination of activated neutrophils. The present review will focus on the molecular regulation of programmed cell clearance, and discuss the role of cell elimination in the resolution of inflammation.

Oxidative lipidomics of hyperoxic acute lung injury: mass spectrometric characterization of cardiolipin and phosphatidylserine peroxidation

Reactive oxygen species have been shown to play a significant role in hyperoxia-induced acute lung injury, in part, by inducing apoptosis of pulmonary endothelium. However, the signaling roles of phospholipid oxidation products in pulmonary endothelial apoptosis have not been studied. Using an oxidative lipidomics approach, we identified individual molecular species of phospholipids involved in the apoptosis-associated peroxidation process in a hyperoxic lung. C57BL/6 mice were killed 72 h after exposure to hyperoxia (100% oxygen). We found that hyperoxia-induced apoptosis (documented by activation of caspase-3 and -7 and histochemical terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling staining of pulmonary endothelium) was accompanied by nonrandom oxidation of pulmonary lipids. Two anionic phospholipids, mitochondria-specific cardiolipin (CL) and extramitochondrial phosphatidylserine (PS), were the two major oxidized phospholipids in hyperoxic lung. Using electrospray ionization mass spectrometry, we identified several oxygenation products in CL and PS. Quantitative assessments revealed a significant decrease of CL and PS molecular species containing C(18:2), C(20:4), C(22:5), and C(22:6) fatty acids. Similarly, exposure of mouse pulmonary endothelial cells (MLEC) to hyperoxia (95% oxygen; 72 h) resulted in activation of caspase-3 and -7 and significantly decreased the content of CL molecular species containing C(18:2) and C(20:4) as well as PS molecular species containing C(22:5) and C(22:6). Oxygenated molecular species were found in the same two anionic phospholipids, CL and PS, in MLEC exposed to hyperoxia. Treatment of MLEC with a mitochondria-targeted radical scavenger, a conjugate of hemi-gramicidin S with nitroxide, XJB-5-131, resulted in significantly lower oxidation of both CL and PS and a decrease in hyperoxia-induced changes in caspase-3 and -7 activation. We speculate that cytochrome c driven oxidation of CL and PS is associated with the signaling role of these oxygenated species participating in the execution of apoptosis and clearance of pulmonary endothelial cells, thus contributing to hyperoxic lung injury.

Involvements of the lipid peroxidation product, HNE, in the pathogenesis and progression of Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder. A number of hypotheses have been proposed to explain AD pathogenesis. One such hypothesis proposed to explain AD pathogenesis is the oxidative stress hypothesis. Increased levels of oxidative stress markers including the markers of lipid peroxidation such as acrolein, 4-hydroxy-2-trans-nonenal (HNE), malondialdehyde, etc. are found in brains of AD subjects. In this review, we focus principally on research conducted in the area of HNE in the central nervous system (CNS) of AD and mild cognitive impairment (MCI), and further, we discuss likely consequences of lipid peroxidation with respect to AD pathogenesis and progression. Based on the research conducted so far in the area of lipid peroxidation, it is suggested that lipid accessible antioxidant molecules could be a promising therapeutic approach to treat or slow progression of MCI and AD.

Comparison of the relative activities of inducing platelet apoptosis stimulated by various platelet-activating agents

Apoptosis-like events are known to occur in anuclear platelets. Although the mechanisms responsible for these events are still not completely understood, studies suggested that some platelet agonists can activate platelet apoptosis. However, the relative activities of various platelet agonists in inducing apoptosis have not yet been investigated. In the present study we explored this issue, and attempted to identify the correlation between platelet activation and apoptosis. In a platelet aggregation study, there were no significant differences respectively stimulated by arachidonic acid (AA; 100 microM), ADP (20 microM), collagen (10 microg/mL), thrombin (0.1 U/mL), U46619 (10 microM), and A23187 (5 microM). In a subsequent study, we fixed these concentrations of agonists to further compare their relative activities in inducing platelet apoptosis. Our results found that thrombin, U46619, and A23187 possess stronger activities than the other agonists in inducing platelet apoptosis (i.e., phosphatidylserine exposure, mitochondrial membrane potential depolarization, eukaryotic initiation factor (eIF)2alpha, and caspase activation). On the other hand, AA induced no apoptotic events in platelets. Based on this approach, we demonstrated for the first time that thrombin, U46619, and A23187, but not AA, possess stronger activity in inducing platelet apoptosis. In addition, we also found that platelet activation might not necessarily be associated with the occurrence of platelet apoptosis. The in vivo physiological function of the apoptotic machinery in platelets is not yet clearly understood, and needs to be further investigated in the future.

Age-related loss of phospholipid asymmetry in APP(NLh)/APP(NLh) x PS-1(P264L)/PS-1(P264L) human double mutant knock-in mice: relevance to Alzheimer disease

Using APP(NLh)/APP(NLh) x PS-1(P246L)/PS-1(P246L) human double knock-in (APP/PS-1) mice, we examined whether phosphatidylserine (PtdSer) asymmetry is significantly altered in brain of this familial Alzheimer disease mouse model in an age-dependent manner as a result of oxidative stress, toxic Abeta(1-42) oligomer production, and/or apoptosis. Annexin V (AV) and NBD-PS fluorescence in synaptosomes of wild-type (WT) and APP/PS-1 mice were used to determine PtdSer exposure with age, while Mg(2+) ATPase activity was determined to correlate PtdSer asymmetry changes with PtdSer translocase, flippase, activity. AV and NBD-PS results demonstrated significant PtdSer exposure beginning at 9 months compared to 1-month-old WT controls for both assays, a trend that was exacerbated in synaptosomes of APP/PS-1 mice. Decreasing Mg(2+) ATPase activity confirms that the age-related loss of PtdSer asymmetry is likely due to loss of flippase activity, more prominent in APP/PS-1 brain. Two-site sandwich ELISA on SDS- and FA-soluble APP/PS-1 brain fractions were conducted to correlate Abeta(1-40) and Abeta(1-42) levels with age-related trends determined from the AV, NBD-PS, and Mg(2+) ATPase assays. ELISA revealed a significant increase in both SDS- and FA-soluble Abeta(1-40) and Abeta(1-42) with age, consistent with PtdSer and flippase assay trends. Lastly, because PtdSer exposure is affected by pro-apoptotic caspase-3, levels of both latent and active forms were measured. Western blotting results demonstrated an increase in both active fragments of caspase-3 with age, while levels of pro-caspase-3 decrease. These results are discussed with relevance to loss of lipid asymmetry and consequent neurotoxicity in brain of subjects with Alzheimer disease.

Toxicity and clearance of intratracheally administered multiwalled carbon nanotubes from murine lung

Carbon nanotubes (CNT) are known to have widespread industrial applications; however, several reports indicated that these compounds may be associated with adverse effects in humans. In this study, multiwalled carbon nanotubes were administered to murine lungs intratracheally to determine whether acute and chronic pulmonary toxicity occurred. In particular, pristine multiwalled carbon nanotubes (PMWCNT) and acid-treated multiwalled carbon nanotubes (TMWCNT) were used in this study. In broncheoalveolar lavage fluid (BALF) cell analysis, PMWCNT induced more severe acute inflammatory cell recruitment than TMWCNT. Histopathologically, both PMWCNT and TMWCNT induced multifocal inflammatory granulomas in a dose-dependent manner. The observed granulomas were reversible, with TMWCNT-induced granulomas diminishing faster than PMWCNT-induced granulomas. Although the area of granuloma reduced with time, hyperplasia and dysplastic characteristics such as mitotic figures, anisokaryosis, and anisocytosis were still observed. These findings demonstrate that MWCNT induces granulomatous inflammation, and the duration and pattern of inflammation seem to vary depending upon the types of MWCNT to which mice are exposed. Therefore, toxicity studies on various types of CNT are needed as the responsiveness to these compounds differs.

The role of nanotoxicology in realizing the 'helping without harm' paradigm of nanomedicine: lessons from studies of pulmonary effects of single-walled carbon nanotubes

Nano-sized materials and nano-scaled processes are widely used in many industries. They are being actively introduced as diagnostic and therapeutic in biomedicine and they are found in numerous consumer products. The small size of nanoparticles, comparable with molecular machinery of cells, may affect normal physiological functions of cells and cause cytotoxicity. Their toxic potential cannot be extrapolated from studies of larger particles due to unique physicochemical properties of nanomaterials. Therefore, the use of nanomaterials may pose unknown risks to human health and the environment. This review discusses several important issues relevant to pulmonary toxicity of nanoparticles, especially single-walled carbon nanotubes (SWCNT), their direct cytotoxic effects, their ability to cause an inflammatory response, and induce oxidative stress upon pharyngeal aspiration or inhalation. Further, recognition and engulfment of nanotubes by macrophages as they relate to phagocytosis and bio-distribution of nanotubes in tissues and circulation are discussed. The immunosuppressive effects of CNT and their significance in increased sensitivity of exposed individuals to microbial infections are summarized. Finally, data on biodegradation of SWCNT by oxidative enzymes of inflammatory cells are presented in lieu of their persistence and distribution in the body.

Possible effects of interferon-alpha on Fas-induced renal apoptosis in mouse

Fas (APO-1/CD95) is a cell surface receptor that initiates apoptotic pathway. Fas-stimulated ROS generation may play important role in Fas-mediated apoptosis. The aim of this study was to evaluate the influence of interferon-alpha on oxidative stress parameters in Fas-induced renal apoptosis in mice kidney.

SUBJECTS AND METHODS

One-month-old Balb C male mice were used for the study. The animals were divided in four groups: group 1 were the controls, group 2 mice were treated with anti-Fas antibody i.p., group 3 mice were treated with IFN-alpha, and group 4 mice were treated with both agents simultaneously. The mice were killed 48 h afterwards, and kidneys were homogenized. TBA reactive substances (TBARS), glutathione content, and reactive carbonyl group (RCG) were measured.

RESULTS

The results showed a statistically significant increase of TBARS (p < 0.05) and RCG (p < 0.05) concentration in the group treated with anti-Fas antibody versus control. IFN-alpha decreased the concentration of TBARS and RCG after anti-Fas antibody administration (p < 0.05). There is no significant difference in glutathione content between investigated groups.

CONCLUSION

IFN-alpha might be considered as a new target for therapeutic intervention in FasL/Fas induced renal injury.

Immune mechanisms in alcoholic liver disease

Growing evidence indicates that inflammatory reactions play an important role in the pathogenesis of alcoholic liver disease (ALD). The implication of immunity in fueling chronic inflammation in ALD has emerged from clinical and experimental evidence showing the recruitment and the activation of lymphocytes in the inflammatory infiltrates of ALD and has received further support by the recent demonstration of a role of Th17 lymphocytes in alcoholic hepatitis. Nonetheless, the mechanisms by which alcohol triggers adaptive immune responses are still incompletely characterized. Patients with advanced ALD show a high prevalence of circulating IgG and T-lymphocytes towards epitopes derived from protein modification by hydroxyethyl free radicals (HER) and end-products of lipid peroxidation. In both chronic alcohol-fed rats and heavy drinkers the elevation of IgG against lipid peroxidation-derived antigens is associated with an increased production of pro-inflammatory cytokines/chemokines and with the severity of histological signs of liver inflammation. Moreover, CYP2E1-alkylation by HER favors the development of anti-CYP2E1 auto-antibodies in a sub-set of ALD patients. Altogether, these results suggest that allo- and auto-immune reactions triggered by oxidative stress might contribute to fuel chronic hepatic inflammation during the progression of ALD.

The liaison between apoptotic cells and macrophages--the end programs the beginning

The efficient execution of apoptotic cell death with the clearance of apoptotic debris by phagocytes is a key regulatory mechanism ensuring tissue homeostasis. Failure in this execution program contributes to the pathogenesis of many human diseases. In this review, we describe the current knowledge regarding the interaction of apoptotic cells with their professional 'captors', the macrophages, with special emphasis on the immunological outcome. Removal of apoptotic cells must be considered as a process that actively delivers signals to polarize macrophages, which are fundamental for the resolution of inflammation. However, the sculpting of macrophage responses by apoptotic cells can be misused under certain inflammatory disease conditions, including tumor development.

Acute Pulmonary Inflammation Induced by Lung Overloading with Selenium Particles: Leukocyte Response andIn SituDetection of Selenium at High Resolution

The kinetics of the acute inflammatory response of the lung was triggered in CD-1 mice by a single intratracheal instillation of a large amount of Se (10 mg); it was studied by quantitative cytology of bronchoalveolar lavage samples, light microscopy, and scanning electron microscopy coupled with x-ray elemental microanalysis. Bronchoalveolar lavage leukocytes were mostly neutrophils and increased from 12 to 24 h of Se treatment and decreased at 72 h. Only less than half of the granulocytes showed ingested Se particles; in contrast, virtually all BAL macrophages contained Se particles. Scanning electron microscopy coupled with X-ray elemental microanalysis revealed that the intracellular Se particles were heterogeneous in size (diameters from 0.4 and up to 14 microm), and that Se inclusions were sometimes accumulated at a pole of the cell. At 72 h after instillation of the particles, Se-loaded alveolar macrophages were migrated in the interstitial space of the alveoli. Se-positive regions had a focal distribution in the lung; accumulation of inflammatory cells erased the alveolar architecture of these areas of the deep lung. Our data indicates that Se overloading of the lung results in: (1) an acute inflammatory response that is dominated by neutrophils; (2) early removal of Se done mostly by alveolar macrophages, and (3) formation of focal areas of invasion of the lung parenchyma by inflammatory infiltrates.

Ovalbumin encapsulation into liposomes results in distinct degrees of oral immunization in mice

Oral administration of protein antigens, such as ovalbumin, may result in induction of either tolerance or immunization. To avoid oral tolerance, there are new strategies to protect the antigens from degradation within the gastrointestinal tract and to allow them to reach inductive immunological sites. One such strategy is the usage of liposomes. Different parameters may influence the stability of liposomes in the gastrointestinal tract. Herein, we studied the immunological consequences of oral administration of liposome-encapsulated ovalbumin in different strains of mice using different liposomes. Our data demonstrated that ovalbumin liposomes improved the induction of oral immunization and the degree of improvement depended on the liposome type and on the strain of mice used. The mechanism responsible for this differential effect of liposomes depended on the site of antigen release and absorption. Therefore, some liposomes might be suitable as adjuvants for oral immunization, others for oral tolerance induction.

A role of phosphatidylserine externalization in clearance of erythrocytes exposed to stress but not in eliminating aging populations of erythrocyte in mice

Age dependent changes in phosphatidylserine (PS) externalization were studied in mouse erythrocytes of different age groups (range 1-55 days) by using a newly developed double in vivo biotinylation (DIB) technique. Around 3-4% of the erythrocytes freshly released in the circulation were PS(+) but this proportion fell rapidly to 1% or less and did not increase at later time points. Blocking erythrocyte clearance from the circulation by in vivo depletion of macrophages (by treatment with clodronate loaded liposomes) for up to 7 days did not result in accumulation of PS(+) erythrocytes in the circulation indicating that the low percentage of PS(+) cells within old erythrocytes (age >40 days) was not related to the clearance of PS(+) erythrocytes by macrophages. In vitro treatment with stress inducing agents like deoxyglucose or Ca(++)/calcium ionophore resulted in a marked induction of PS externalization in mouse erythrocytes and this effect was most prominent in the youngest erythrocyte population (age <10 days). Kinetics of clearance of different age groups of stress exposed erythrocytes after intravenous infusion into recipient mice indicated that the young erythrocytes were cleared at fastest rate from the circulation as compared to erythrocytes of older age groups. Within young erythrocytes exposed to stress, PS(+) erythrocytes were preferentially cleared. Taken together our results suggest that PS externalization is unlikely to have a role in the removal of old erythrocytes from blood circulation but may have a role in the clearance of stressed and damaged young erythrocytes in blood circulation.

Tocopherols and tocotrienols in membranes: a critical review

The familiar role of tocols (tocopherols and tocotrienols) as lipid-soluble chain-terminating inhibitors of lipid peroxidation is currently in the midst of a reinterpretation. New biological activities have been described for tocols that apparently are not dependent on their well-established antioxidant behaviour. These activities could well be real, but there remain large gaps in our understanding of the behaviour of tocols in membranes, especially when it comes to the alpha-, beta-, gamma-, delta-chroman methylation patterns and the seemingly special nature of tocotrienols. It is inappropriate to make conclusions and develop models based on in vivo (or cell culture) results with reference to in vitro measurements of antioxidant activity. When present in biological membranes, tocols will experience a large variation in the local composition of phospholipids and the presence of neutral lipids such as cholesterol, both of which would be expected to change the efficiency of antioxidant action. It is likely that tocols are not homogeneously dispersed in a membrane, but it is still not known whether any specific combination of lipid head group and acyl chains are conferred special protection from peroxidation, nor do we currently appreciate the structural role that tocols play in membranes. Tocols may enhance curvature stress or counteract similar stresses generated by other lipids such as lysolipids. This review will outline what is known about the location and behaviour of tocols in phospholipid bilayers. We will draw mainly from the biophysical literature, but will attempt to extend the discussion to biologically relevant phenomena when appropriate. We hope that it will assist researchers when designing new experiments and when critically assessing the results, in turn providing a more thorough understanding of the biochemistry of tocols.

Interplay between oxidative stress and immunity in the progression of alcohol-mediated liver injury

Inflammation is recognized increasingly as having an important role in the pathogenesis of alcoholic liver disease (ALD). Nonetheless, the mechanisms by which alcohol maintains hepatic inflammation are still characterized incompletely. Several studies have demonstrated that ethanol-induced oxidative stress promotes immune responses in ALD by stimulating both humoral and cellular reactions against liver proteins adducted to hydroxyethyl free radicals and several lipid peroxidation products. Moreover, ALD patients have autoantibodies targeting cytochrome P4502E1 and oxidized phospholipids. In both chronic alcohol-fed rats and heavy drinkers, the elevation of IgG against lipid peroxidation-derived antigens is associated with tumor necrosis factor-alpha production and the severity of liver inflammation. On this basis, we propose that allo- and autoimmune reactions associated with oxidative stress might contribute to fueling hepatic inflammation in ALD.

Oxidative lipidomics of programmed cell death

Oxidized phospholipids play an important role in execution of the mitochondrial stage of apoptosis and clearance of apoptotic cells by macrophages. Therefore, the identification and quantification of oxidized phospholipids generated during apoptosis are very important. These can be achieved successfully by a newly developed approach--oxidative lipidomics, including a combination of electrospray ionization/mass spectrometry (ESI-MS) and fluorescence high-performance liquid chromatography techniques. Using oxidative lipidomics allows the quantification of specific phospholipids and their hydroperoxides. We characterized selective oxidation of two anionic phospholipids: cardiolipin (CL) in mitochondria and phosphatidylserine (PS) outside of mitochondria. ESI-MS analysis of cytochrome c/H(2)O(2)-driven tetralinoleoyl-CL (TLCL) oxidized molecular species demonstrated accumulation of products monohydroxy-TLCL; monohydroxy-monohydroperoxy-TLCL, monohydroxy-dihydroperoxy-TLCL, monohydroxy-trihydroperoxy-TLCL; and monohydroxy-tetrahydroperoxy-TLCL. We explored the application of oxidative lipidomics in a number of conditions in both in vitro and in vivo models where there is a known contribution of apoptosis and/or inflammation. Accumulation of CL hydroperoxides, originated from molecular species of CL containing C(22:6) after experimental traumatic brain injury, was shown. ESI-MS analysis of intestine CL in mouse after gamma-irradiation detected several CL oxidized molecular species: (C(18:2))(3)/(C(18:2+OOH)); (C(18:2))(2)/(C(18:2+OOH))(2); (C(18:2))(1)/(C(18:2+OOH))(3); and (C(18:2+OOH))(4). ESI-MS analysis and tandem MS/MS experiments revealed that PS with oxidized C(22:6) [m/z866 (C(18:0)/C(22:6+OOH)) originated from the ion at m/z 834 (C(18:0)/C(22:6))] was the major oxidized molecular species in the tested models in vitro and in vivo, including (1) cytochrome c/H(2)O(2) catalyzed oxidation of rat brain PS; (2) after experimental traumatic rat brain injury in rats, (3) in postmortem brain samples from patients with Alzheimer's disease, and (4) in the small intestine in gamma-irradiated mouse. We conclude that oxidative lipidomics is a powerful technique to study lipid oxidation and its role in cell death across a spectrum of tissues and insults.

Mediation of apoptosis by oxidized phospholipids

Free radical-mediated oxidation of (poly)unsaturated glycerophospholipids in membranes and lipoproteins leads to the formation of a plethora of products. Some of these oxidized phospholipids, especially the truncated forms, induce apoptosis depending on their chemical structure, concentration and cell type. Depending on the phospholipid and the cell type, two pathways have so far been identified for the intracellular transmission of the apoptotic signals. One pathway involves activation of acid sphingomyelinase, which gives rise to the formation of ceramide and is followed by phosphorylation of pro-apoptotic mitogen-activated protein kinases. Alternatively, oxidized phospholipids act directly on mitochondria leading to efflux of pro-apoptotic effectors in endothelial cells. During the execution of the apoptotic program additional oxidized phospholipids are generated. The apoptotic cascade itself leads to oxidation and exposure of e.g. membrane phosphatidylserine. Oxidized phospholipids on the outer leaflet of the plasma membrane can form surface lipid patterns that specifically bind to phagocytic cells, e.g. macrophages.In this manuscript we review the recent literature reporting on apoptosis-inducing glycerophospholipids. In addition, we describe the cellular processes that lead to phospholipid oxidation as part of the apoptotic mode of cell death and are likely to enhance the recognition of apoptotic cells by phagocytic macrophages.

Loss of phospholipid asymmetry and elevated brain apoptotic protein levels in subjects with amnestic mild cognitive impairment and Alzheimer disease

Oxidative stress, a hallmark of Alzheimer disease (AD), has been shown to induce lipid peroxidation and apoptosis disrupting cellular homeostasis. Normally, the aminophospholipid phosphatidylserine (PtdSer) is asymmetrically distributed on the cytosolic leaflet of the lipid bilayer. Under oxidative stress conditions, asymmetry is altered, characterized by the appearance of PtdSer on the outer leaflet, to initiate the first stages of an apoptotic process. PtdSer asymmetry is actively maintained by the ATP-dependent translocase flippase, whose function is inhibited if covalently bound by lipid peroxidation products, 4-hydroxynonenal (HNE) and acrolein, within the membrane bilayer in which they are produced. Additionally, pro-apoptotic proteins Bax and caspase-3 have been implemented in the oxidative modification of PtdSer resulting in subsequent asymmetric collapse, while anti-apoptotic protein Bcl-2 has been found to prevent this process. The current investigation focused on detection of PtdSer on the outer leaflet of the bilayer in synaptosomes from brain of subjects with AD and amnestic mild cognitive impairment (MCI), as well as expression levels of apoptosis-related proteins Bcl-2, Bax, and caspase-3. Fluorescence and Western blot analysis suggest PtdSer exposure on the outer leaflet is significantly increased in brain from subjects with MCI and AD contributing to early apoptotic elevation of pro- and anti-apoptotic proteins and finally neuronal loss. MCI is considered a possible transition point between normal cognitive aging and probable AD. Brain from subjects with MCI is reported to have increased levels of tissue oxidation; therefore, the results of this study could mark the progression of patients with MCI into AD. This study contributes to a model of apoptosis-specific oxidation of phospholipids consistent with the notion that PtdSer exposure is required for apoptotic-cell death.

Lifespan of etoposide-treated human neutrophils is affected by antioxidant ability of quercetin

Neutropenia is the primary dose-limiting effect of etoposide toxicity resulting in a decreased efficiency of cancer treatment. Hence, the protection of neutrophils has important clinical implications. We investigated whether quercetin, due to its antioxidant properties, is able to modulate the damaging activity of etoposide. DNA damage, evaluated by the comet assay, and apoptosis, determined by FACScan flow cytometry using Annexin/PI, increased with etoposide doses. The intracellular level of reactive oxygen species (ROS) was enhanced in resting neutrophils incubated with etoposide at concentrations up to 25 microM; above this concentration etoposide revealed antioxidant properties. Only in latex-activated neutrophils, i.e. with latex-stimulated respiratory burst was the ROS production inhibited, as assessed by the luminol amplified chemiluminescence. The characteristic electron spin resonance (ESR) signal of etoposide phenoxyl radical, which occurs in the presence of myeloperoxidase, H2O2 and etoposide, was quenched by quercetin in a dose-dependent manner (0.1-0.5 microM). Quercetin also inhibited DNA damage induced by etoposide and enhanced the inhibitory action of etoposide on the ROS formation in neutrophils. However, quercetin (1 microM) lowered early and late apoptosis/necrosis only when apoptosis was induced by 25 microM etoposide; at higher etoposide concentration apoptosis was enhanced. Summing up, antioxidant adjuvant therapy using quercetin can be beneficial in prolonging neutrophils' lifespan in peripheral blood only when etoposide plasma concentration is low.